15 char­ac­ters are ran­domly gen­er­ated on each refresh. I tried to push a bit the num­bers : it’s fine until 50 char­ac­ters, but starts to be real slow after. 200 or more char­ac­ters is just incred­i­bly slow, and may even crash the browser…

Maybe there is a less CPU inten­sive way to deal with this ? I didn’t man­age to include it directly into the char­ac­ters ani­ma­tion func­tion…
My code is pretty messy, but if you’re curi­ous it’s here.